SUBROUTINE calc_liquid_water_content

!--------------------------------------------------------------------------------!
! This file is part of PALM.
!
! PALM is free software: you can redistribute it and/or modify it under the terms
! of the GNU General Public License as published by the Free Software Foundation,
! either version 3 of the License, or (at your option) any later version.
!
! PALM is distributed in the hope that it will be useful, but WITHOUT ANY
! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
! A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
!
! You should have received a copy of the GNU General Public License along with
! PALM. If not, see <http://www.gnu.org/licenses/>.
!
! Copyright 1997-2014 Leibniz Universitaet Hannover
!--------------------------------------------------------------------------------!
!
! Current revisions:
! -----------------
!
!
! Former revisions:
! -----------------
! $Id: calc_liquid_water_content.f90 1310 2014-03-14 08:01:56Z raasch $
!
! 1253 2013-11-07 10:48:12Z fricke
! Bugfix: q is set to qr in case that q is smaller than qr
!
! 1115 2013-03-26 18:16:16Z hoffmann
! drizzle can be used independently from precipitation
!
! 1053 2012-11-13 17:11:03Z hoffmann
! description expanded to the two-moment cloud scheme
!
! 1036 2012-10-22 13:43:42Z raasch
! code put under GPL (PALM 3.9)
!
! 667 2010-12-23 12:06:00Z suehring/gyschka
! nxl-1, nxr+1, nys-1, nyn+1 replaced by nxlg, nxrg, nysg, nyng
!
! 95 2007-06-02 16:48:38Z raasch
! hydro_press renamed hyp
!
! 19 2007-02-23 04:53:48Z raasch
! Old comment removed
!
! RCS Log replace by Id keyword, revision history cleaned up
!
! Revision 1.5  2005/03/26 15:22:06  raasch
! Arguments for non-cyclic boundary conditions added to argument list of
! routine exchange_horiz,
! ql calculated for the ghost points, exchange of ghost points removed
!
! Revision 1.1  2000/04/13 14:50:45  schroeter
! Initial revision
!
!
!
! Description:
! ------------
! Calculation of the liquid water content (0%-or-100%-scheme). This scheme is 
! used by the one and the two moment cloud physics scheme. Using the two moment 
! scheme, this calculation results in the cloud water content.
!------------------------------------------------------------------------------!


    USE arrays_3d
    USE cloud_parameters
    USE constants
    USE control_parameters
    USE grid_variables
    USE indices
    USE pegrid

    IMPLICIT NONE

    INTEGER :: i, j, k

    REAL :: alpha, e_s, q_s, t_l

    DO  i = nxlg, nxrg
       DO  j = nysg, nyng
          DO  k = nzb_s_inner(j,i)+1, nzt

!
!--          Compute the liquid water temperature
             t_l = t_d_pt(k) * pt(k,j,i)

!
!--          Compute saturation water vapor pressure at t_l
             e_s = 610.78 * EXP( 17.269 * ( t_l - 273.16 ) / &
                                          ( t_l - 35.86 ) )

!
!--          Compute approximation of saturation humidity
             q_s = 0.622 * e_s / ( hyp(k) - 0.378 * e_s )

!
!--          Correction factor
             alpha = 0.622 * l_d_r * l_d_cp / ( t_l * t_l )

!
!--          Correction of the approximated value
!--          (see: Cuijpers + Duynkerke, 1993, JAS, 23)
             q_s = q_s * ( 1.0 + alpha * q(k,j,i) ) / ( 1.0 + alpha * q_s )

!
!--          Compute the liquid water content
             IF ( icloud_scheme == 0  .AND.  precipitation)  THEN
                IF ( ( q(k,j,i) - q_s - qr(k,j,i) ) > 0.0 ) THEN
                   qc(k,j,i) = q(k,j,i) - q_s - qr(k,j,i)
                   ql(k,j,i) = qc(k,j,i) + qr(k,j,i)
                ELSE
                   IF ( q(k,j,i) < qr(k,j,i) )  q(k,j,i) = qr(k,j,i)
                   qc(k,j,i) = 0.0 
                   ql(k,j,i) = qr(k,j,i)
                ENDIF
             ELSEIF ( icloud_scheme == 0  .AND.  .NOT. precipitation )  THEN
                IF ( ( q(k,j,i) - q_s ) > 0.0 ) THEN
                   qc(k,j,i) = q(k,j,i) - q_s
                   ql(k,j,i) = qc(k,j,i)
                ELSE
                   qc(k,j,i) = 0.0 
                   ql(k,j,i) = 0.0
                ENDIF
             ELSE
                IF ( ( q(k,j,i) - q_s ) > 0.0 ) THEN
                   ql(k,j,i) = q(k,j,i) - q_s
                ELSE
                   ql(k,j,i) = 0.0 
                ENDIF
             ENDIF
          ENDDO
       ENDDO
    ENDDO
    
 END SUBROUTINE calc_liquid_water_content